This type of washing and drying machine includes a washing and drying machine comprising a drum rotated about a horizontal axis and a washing and drying machine comprising an inner tub rotated about a vertical axis. Each of the drum and the inner tub has a circumferential wall formed with a number of small holes and functions as a rotating tub. These washing and drying machines have a similar washing function and a similar drying function. For example, in a drying step, drying warm air is supplied by circulation while the rotating tub is rotated at low speeds, so that laundry accommodated in the rotating tub is dried. A water tub (outer tub) capable of storing water is provided outside the rotating tub. The washing and drying machine carries out washing with the water tub storing water.
When a water-supplying operation is continued even after supplied water exceeds a predetermined water level owing to failure in water supply or a control device of a water-supply valve, for example, water overflows such that there is a possibility that electrical components may be drenched and the floor may become sloppy. In view of the problem, the water tub is formed with overflow outlets through which overflowed water is directly discharged out of the machine when the water level in the water tub exceeds a predetermined level. On the other hand, the aforesaid drying warm air is adapted to be circulated through the water tub. Accordingly, the overflow outlets are located so that overflowed water is discharged through the overflow outlets before entering an outlet and an inlet of warm air, as in a washing and drying machine described in Japan published patent application No. 2005-46414 (JP-A-2005-46414).
FIG. 7 illustrates an example of conventional drum washing and drying machine of this type. This washing and drying machine includes a casing 1 in which a water tub 2 is elastically suspended. A drum 3 is provided in the water tub 2 so as to be rotatable about a transverse axis in a slightly inclined state. The casing 1 has a front formed with an access opening 1a through which laundry is put into and taken out of the drum 3. The access opening 1a is watertightly connected via elastic bellows 4 to an opening end provided in the front of the water tub 2. The access opening 1a is adapted to be opened and closed by a pivotally mounted door 5. An electric motor 6 is mounted on a rear of the water tub 2 and has a rotational shaft which is directly connected to a rear of the drum 3. Accordingly, rotative power of the motor 6 is directly transmitted to the drum 3. Furthermore, a drain conduit 7 with a midway drain valve 8 is provided on the bottom of the water tub 2. The drain conduit 7 is introduced outside the casing 1 (the washing and drying machine) so that water in the water tub 2 is drained through the drain valve 8 to a predetermined drainage location.
An air supply duct 9 has an upper end connected to the upper rear of the water tub 2. An exhaust duct 10 has an upper end connected to the front of the water tub 2. The air supply duct 9 and the exhaust duct 10 have respective lower ends which are connected to each other by a heat exchange duct 11 provided with a warm air generating unit so as to communicate with each other. The warm air generating unit comprises a known heat pump mechanism 40.
The heat pump mechanism 40 is adapted to pump refrigerant by a compressor 13 and to circulate the refrigerant through a condenser 14, a capillary tube (serving as a refrigerant throttle valve) and an evaporator 15 sequentially. The condenser 14 heat-exchanges air circulated in the heat exchange duct 11, thereby heating the air. A blower 16 supplies the air heated by the condenser 14 through the air supply duct 9 into the water tub 2 and the drum 3 as warm air. As a result, laundry in the drum 3 is dried. Air used for drying and containing water content is cooled by the evaporator 15 thereby to be dehumidified. The air is then heated by the condenser 14 and re-supplied as drying warm air into the drum 3. That is, drying air is supplied into the drum 3 to dry laundry while being circulated in the circulation air passage 12 as shown by arrow A in FIG. 7.
An overflow outlet 17 is provided at a predetermined position in a rear wall of the water tub 2 in order to cope with abnormal overflow water such as described above. The predetermined position is set so as to be located lower than a connecting hole of the air supply duct 9 serving an outlet of the circulation air passage 12 and a connecting hole of the exhaust duct 10 serving as an inlet of the circulation air passage 12. The overflow outlet 17 is constructed so that overflowed water caused to flow therethrough is directly discharged outside the machine through a drain passage such as an overflow conduit 18 and a drain conduit 7. A water supply conduit 20 is provided on an upper part of the water tub 2 so as to communicate with the water tub 2. The water supply conduit 20 includes a water supply valve 19 connected to a water supply. The water supply conduit 20 is capable of supplying water into the water tub 2 and the drum 3.
According to the foregoing construction, water in the water tub 2 is discharged outside the machine through the overflow outlet 17 before entering the circulation air passage 12 even when water supply to the water tub 2 is in an abnormal condition. Accordingly, a water level in the water tub 2 is prevented from being increased to or above a predetermined level. On the other hand, in the drying step, warm air is generated the heat pump mechanism 40 disposed in the heat exchange duct 11. The warm air is supplied through the air supply duct 9 from the rear side of the water tub 2 into the drum 3. In this case, the pressure in the water tub 2 is increased by the circulated warm air. When the heat pump mechanism 40 is employed as a warm air generating unit, a temperature of the warm air tends to be lower than in the case where an electric heater is employed. Accordingly, a cooling performance of the compressor 13 needs to be increased to about 1500 W, for example, and a flow rate of circulated air also needs to be increased to about 3 m.sup.3/min, for example. As a result, the inner pressure of the water tub 2 tends to be further increased.
In the drying step, an efficient drying operation is desired by making use of a closed space including the circulation air passage 12 with the circulation air flowing through the water tub 2. However, since the aforesaid overflow outlet 17 normally communicates with the exterior of the machine through the drain passage such as the overflow conduit 18, part of warm air leaks through the overflow outlet 17 out of the machine during the drying step, resulting in loss of heat energy. The heat energy loss becomes more significant as the inner pressure of the water tub 2 is increased as described above.
Furthermore, as shown in FIG. 7, the front side of the water tub 2 has a positional limitation due to the access opening 1a or the like. Accordingly, the overflow outlet 17 is normally formed at the rear side of the water tub 2. However, since supply of warm air is also carried out on the rear of the water tub 2, part of the warm air supplied through the air supply duct 9 tends to flow to the overflow outlet 17 side before supplied into the drum 3 (as shown by broken arrow B in FIG. 7), whereupon the warm air leaks out of the machine. Thus, leak of part of warm air prevents improvement in the drying efficiency. Furthermore, when part of warm air is discharged into a room where the washing and drying machine is installed, the temperature and humidity in a residential space are increased. Laundry contains a large amount of water particularly in a first half of the drying step. As a result, the humidity of the warm air discharged out of the machine is increased, resulting in discomfort of the user.
An object of the present invention is to provide a washing and drying machine which can carry out an efficient drying operation without damaging the original function of the overflow outlet by preventing warm air from leaking during the drying step.